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Browse Prior Art Database

Trapped Flux Removal

IP.com Disclosure Number: IPCOM000097210D
Original Publication Date: 1962-Jul-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Caswell, HL: AUTHOR [+3]

Abstract

Magnetic flux is unintentionally trapped in the shielding ground plane of a superconductive circuit. This occurs either as a result of the incomplete expulsion of stray magnetic fields at the time the circuit is initially cooled below the superconducting critical temperature or during circuit operation, when a portion of the ground plane is driven resistive. In either event, the trapped flux provides an unwanted magnetic field that can adversely affect the circuit cryotrons in proximity. By providing a ground plane that exhibits a linear thickness variation in one dimension, any trapped flux is caused to migrate to a region where it does not influence the operating superconductive circuit.

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Trapped Flux Removal

Magnetic flux is unintentionally trapped in the shielding ground plane of a superconductive circuit. This occurs either as a result of the incomplete expulsion of stray magnetic fields at the time the circuit is initially cooled below the superconducting critical temperature or during circuit operation, when a portion of the ground plane is driven resistive. In either event, the trapped flux provides an unwanted magnetic field that can adversely affect the circuit cryotrons in proximity. By providing a ground plane that exhibits a linear thickness variation in one dimension, any trapped flux is caused to migrate to a region where it does not influence the operating superconductive circuit.

In this arrangement, the ground plane tapers from left to right and includes a number of trapped flux lines 1 through a normal region N. The circles and crosses represent circulating current. The volume occupied by the normal region decreases, if it moves in the direction of the arrow, as a result of the thickness variation in the ground plane. Thus, a net force, proportional to the gradient in thickness and the free energy difference between normal and superconducting states, is present tending to sweep the trapped flux out of the ground plane.

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